CN108802620B

CN108802620B - Vehicle-mounted battery system and method for estimating deterioration of battery over time

Info

Publication number: CN108802620B
Application number: CN201810384925.9A
Authority: CN
Inventors: 高桥贤司; 赤松一志; 町田清仁
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2017-04-27
Filing date: 2018-04-26
Publication date: 2021-06-08
Anticipated expiration: 2038-04-26
Also published as: KR20180120589A; BR102018007917A2; CN108802620A; EP3410138B1; JP6939057B2; US10802080B2; US20180313906A1; KR102019356B1; RU2680660C1; EP3410138A1; JP2018185259A

Abstract

The present disclosure relates to a vehicle-mounted battery system and a method for estimating deterioration of a battery over time. The battery system includes: a battery; a voltage detector that detects a voltage of the battery as a detected voltage value; a current detector that detects a current flowing in the battery as a detected current value; and an electronic control unit. The electronic control unit is configured to estimate the aged deterioration of the battery based on an open-circuit voltage value calculated from the detected voltage value and a current integrated value calculated from the detected current value, and to estimate the aged deterioration of the battery based on the open-circuit voltage value and the current integrated value calculated when the charging rate of the battery is within the non-hysteresis region.

Description

Vehicle-mounted battery system and method for estimating deterioration of battery over time

Technical Field

The present specification discloses a battery system including a rechargeable battery mounted on a vehicle and having a function of estimating the aged deterioration of the battery, and a method of estimating the aged deterioration of the battery.

Background

An electric vehicle equipped with a rotating electric machine as one of driving sources is widely known. This electrically powered vehicle is equipped with a battery system having a rechargeable battery. The secondary battery supplies electric power to the rotating electric machine when the rotating electric machine is driven as a motor, and stores electric power generated when the rotating electric machine is driven as a generator. The battery system controls charging and discharging Of the secondary battery so that a charging rate Of the secondary battery, a so-called State Of Charge (SOC), does not exceed a predetermined upper limit value (sufficiently lower than 100%) nor fall below a predetermined lower limit value (sufficiently higher than 0%). In order to perform such control, it is desirable in a battery system that the charging rate of the secondary battery can be accurately estimated.

In general, the charging rate of the secondary battery can be calculated by referring to a previously stored SOC-OCV curve, the full charge capacity of the secondary battery, and the like. Further, the OCV is an abbreviation of Open Circuit Voltage, which means Open Circuit Voltage. The SOC-OCV curve is a curve showing an open circuit voltage value (OCV) of the secondary battery with respect to the charging rate. For example, if the open-circuit voltage value of the secondary battery can be obtained, the battery system estimates the current charging rate by comparing the open-circuit voltage value with the SOC-OCV curve. In another embodiment, the battery system calculates an integrated value of current input/output to/from the secondary battery, and estimates the amount of change in the charging rate and thus the current charging rate based on a comparison between the integrated value of current and the full charge capacity.

In this way, since the state of charge of the secondary battery is estimated with reference to the SOC-OCV curve and/or the full charge capacity, the stored SOC-OCV curve and/or the full charge capacity are required to accurately show the current state of the secondary battery in order to accurately estimate the state of charge. However, the full charge capacity and/or the change characteristics of the open circuit voltage with respect to the charging rate of the secondary battery gradually change with the aged deterioration of the secondary battery. Therefore, in order to accurately estimate the charging rate, it is desirable to appropriately estimate the aged deterioration of the secondary battery and correct the SOC-OCV curve and the full charge capacity according to the estimation result.

In order to estimate the deterioration of a secondary battery over time, various techniques have been proposed. For example, japanese patent laid-open publication No. 2015-121444 discloses a technique of estimating a full charge capacity based on an open-circuit voltage value and a current integrated value. Specifically, the following technique is disclosed in japanese patent laid-open No. 2015-: during the charging of the secondary battery, the open circuit voltage value is detected twice, and the current integrated value between the two detections is acquired, and the SOC at each detection is obtained as the first SOC and the second SOC based on the open circuit voltage value, and the value obtained by dividing the current integrated value by the difference between the first SOC and the second SOC is calculated as the full charge capacity.

Further, japanese patent application laid-open No. 5537236 discloses a technique for searching for three degradation parameters indicating open circuit voltage characteristics, that is, open circuit voltage variation characteristics with respect to the full charge capacity of a secondary battery. Specifically, in japanese patent application laid-open No. 5537236, an actual measurement value of the open voltage characteristic is acquired by actually measuring the open voltage value and the current integrated value of the secondary battery, and three degradation parameters matching the actual measurement value of the open voltage characteristic are searched for.

Disclosure of Invention

As described above, the conventional technology estimates the aged deterioration of the secondary battery based on the correlation between the actually measured open circuit voltage value and the current integrated value. However, in the secondary battery, a significant hysteresis occurs in which the open-circuit voltage value is different by a certain amount or more from the value of the charging rate after the continuous charging and after the continuous discharging in a part of the charging rate range. It is known that: for example, in the case of a lithium ion secondary battery in which the negative electrode active material contains a silicon-based material (e.g., Si and/or SiO) and graphite, in the low SOC region, even if the SOC is the same, a difference occurs between the open circuit voltage value after continuous charging and the open circuit voltage value after continuous discharging. In the estimation of the aged deterioration, the actual measurement value of the open circuit voltage value is used as described above, but when the open circuit voltage value is acquired within the charging rate range in which significant hysteresis occurs, it is difficult to uniquely identify the aged deterioration from the open circuit voltage value.

In view of the above, the present specification discloses a battery system and an aged deterioration estimation method of a battery, which can easily and accurately estimate aged deterioration even in a battery in which significant lag occurs in a part of a charging rate range.

An exemplary aspect of the present invention is a battery system mounted on a vehicle. The battery system includes: a battery mounted on the vehicle and configured to be charged and discharged, wherein a charging rate range of the battery includes a hysteresis range in which a significant hysteresis occurs, the significant hysteresis being a hysteresis in which an open circuit voltage with respect to a charging rate of the battery has a certain or greater difference between after continuous charging and after continuous discharging, and a non-hysteresis range in which the significant hysteresis does not occur; a voltage detector configured to detect a voltage of the battery as a detected voltage value; a current detector configured to detect a current flowing in the battery as a detected current value; and an electronic control unit configured to control charging and discharging of the battery. The electronic control unit is configured to estimate the aged deterioration of the battery based on an open-circuit voltage value calculated from the detected voltage value and a current integrated value calculated from the detected current value. The electronic control unit is configured to estimate the aged deterioration of the battery based on the open-circuit voltage value and the current integrated value calculated when the charging rate of the battery is within the non-hysteresis region

According to this battery system, the open-circuit voltage value and the current integrated value for estimating the aged deterioration of the battery are acquired when the charging rate is within the non-hysteresis region. Therefore, the aged deterioration can be estimated without being affected by a significant delay. As a result, the deterioration with age can be estimated easily and accurately.

The open circuit voltage value may include a first open circuit voltage value and a second open circuit voltage value acquired in the non-hysteresis region, and the integrated current value may be a value obtained by integrating current values detected from the first open circuit voltage value until the current value changes to the second open circuit voltage value, and the electronic control unit may be configured to estimate at least one of a current full charge capacity of the battery and a change characteristic of the open circuit voltage value with respect to the charge rate as the characteristic indicating the aged deterioration, based on the first open circuit voltage value, the second open circuit voltage value, and the integrated current value.

The full charge capacity of the battery and the variation characteristics of the open circuit voltage value with respect to the charging rate are used for estimating the charging rate of the battery. By estimating the value used for estimating the state of charge, the state of charge of the battery can be estimated with high accuracy.

The battery system may also further include a charger that charges the battery during a stop of the vehicle. The electronic control unit may be configured to temporarily stop charging by the charger when the charging rate of the battery reaches a first charging rate or a second charging rate in the non-hysteresis region during charging of the battery by the charger, and acquire the detected voltage value obtained during a charging stop period as the first open voltage value or the second open voltage value.

With this configuration, the open-circuit voltage value and the current integrated value used for estimating the aged deterioration of the battery can be reliably obtained.

The electronic control unit may be configured to acquire, as the first open voltage value and the second open voltage value, two open voltage values acquired at a timing when the open voltage value is within the non-hysteresis region and can be acquired during a period in which a power source of the vehicle is turned on.

With this configuration, the open-circuit voltage value and the current integrated value used for estimating the aged deterioration of the battery can be obtained even during the power-on period of the vehicle.

The electronic control unit may be configured to control charging and discharging of the battery so that a charging rate of the battery shifts to the non-hysteresis region and acquire the first open-circuit voltage value, the second open-circuit voltage value, and the integrated current value when an elapsed time from last estimation of aged deterioration becomes equal to or longer than a predetermined reference time.

The electronic control unit may be configured to estimate, as the characteristic indicating the aged deterioration, at least a change characteristic of the open-circuit voltage value with respect to the charging rate; estimating a state of charge range to be the non-hysteresis region based on the estimated change characteristic of the open circuit voltage value with respect to the state of charge; updating the non-hysteresis region based on the estimated charge rate range.

With this configuration, a non-hysteresis region corresponding to the current battery state can always be obtained.

The electronic control unit may be configured to update one of the ranges of the charging rate and the charging rate at the time of acquiring the open-circuit voltage value and the current integrated value for estimating the aged deterioration in accordance with the update of the non-hysteresis region.

With this configuration, the open-circuit voltage value and the current integrated value used for estimating the aged deterioration of the battery can be acquired at more appropriate timings, so that the estimation of the aged deterioration can be more improved and the chance of estimating the aged deterioration can be more reliably obtained.

The battery may be a lithium ion secondary battery in which the negative electrode active material contains at least a silicon-based material and graphite, and the charge rate range of the non-hysteresis region may be higher than the charge rate range of the hysteresis region.

By using this battery, high capacity can be achieved.

The battery may be a lithium ion secondary battery in which the negative electrode active material contains at least a silicon-based material and a lithium titanate, and the charge rate range of the non-hysteresis region may be lower than the charge rate range of the hysteresis region.

An exemplary embodiment of the present invention is a method for estimating aged deterioration of a battery system. The charge rate range of the battery includes a hysteresis region that is a charge rate range in which significant hysteresis occurs, the significant hysteresis being hysteresis in which there is some or more difference in an open circuit voltage with respect to the charge rate of the battery after continuous charging and after continuous discharging, and a non-hysteresis region that is a charge rate range in which the significant hysteresis does not occur, the battery system including an electronic control unit. The method for estimating chronological deterioration includes: acquiring a parameter by which an open circuit voltage value between two points and a current integrated value between the two points are calculated when a charging rate of the secondary battery is within the non-hysteresis region; and estimating, by the electronic control unit, the aged deterioration of the battery based on the acquired open-circuit voltage value and the current integrated value.

According to this method of estimating aged deterioration, the open-circuit voltage value and the current integrated value used for estimating aged deterioration of the battery are acquired when the charging rate is in the non-hysteresis region. Therefore, the aged deterioration can be estimated without being affected by a significant delay. As a result, the deterioration with age can be estimated easily and accurately.

According to the battery system and the method for estimating the aged deterioration of the battery disclosed in the present specification, the open-circuit voltage value and the current integrated value used for estimating the aged deterioration of the battery are acquired when the charging rate is in the non-hysteresis region. Therefore, the aged deterioration can be estimated without being affected by a significant delay. As a result, the deterioration with age can be estimated easily and accurately.

Drawings

Features, advantages and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals denote like parts, and in which:

fig. 1 is a diagram showing a configuration of an electric vehicle equipped with a battery system.

Fig. 2 is a diagram showing an example of the SOC-OCV curve.

Fig. 3 is a flowchart illustrating an example of the aged deterioration estimation process of the battery.

Fig. 4A is a flowchart showing a part of an example of the parameter acquisition routine.

Fig. 4B is a flowchart showing a part of an example of the parameter acquisition routine.

Fig. 5 is a diagram showing a working example of the parameter acquisition routine of fig. 4A and 4B.

Fig. 6 is a flowchart showing another example of the parameter acquisition routine.

Fig. 7 is a diagram showing a working example of the parameter acquisition routine of fig. 6.

Fig. 8A is a flowchart showing a part of another example of the parameter acquisition routine.

Fig. 8B is a flowchart showing a part of another example of the parameter acquisition routine.

Fig. 9 is a diagram showing a working example of the parameter acquisition routine of fig. 8A and 8B.

Fig. 10 is a flowchart showing an example of the deterioration estimation routine.

Fig. 11 is a flowchart showing another example of the deterioration estimation routine.

Fig. 12 is a graph showing a change characteristic of the open-circuit voltage according to a change in the local charging rate of the lithium-ion secondary battery.

Fig. 13 is a diagram showing a change in the open circuit potential of the positive electrode accompanying a decrease in the positive electrode capacity of the lithium ion secondary battery, and a change in the open circuit potential of the negative electrode accompanying a decrease in the negative electrode capacity.

Fig. 14 is a diagram illustrating a deviation in the composition correspondence between the positive electrode and the negative electrode of the lithium-ion secondary battery.

Fig. 15 is a diagram illustrating a deviation in the composition due to deterioration of the lithium ion secondary battery.

Fig. 16 is a graph showing a change in open circuit voltage with respect to the battery capacity of the lithium-ion secondary battery (open circuit voltage curve).

Fig. 17 is an explanatory diagram of the voltage error Δ V.

Fig. 18 is a diagram illustrating a change in the hysteresis occurrence point associated with deterioration of the lithium ion secondary battery.

Fig. 19 is a flowchart showing an example of the non-hysteresis region estimation routine.

Detailed Description

The structure of the battery system 10 will be described below with reference to the drawings.

Fig. 1 is a diagram showing a schematic configuration of an electric vehicle 100 equipped with a battery system 10. The electric powered vehicle 100 is a hybrid vehicle including two rotating electric machines MG1 and MG2 and one engine 104 as power sources. However, the battery system 10 disclosed in the present specification may be mounted on a vehicle of another form if it is an electric vehicle. For example, the battery system 10 may be mounted on an electric vehicle having only a rotating electric machine as a power source.

The engine 104 is connected to a power split mechanism 106 including a planetary gear and the like. The planetary gear dividedly transmits the power of the engine 104 to the drive wheels 108 and the first rotating electrical machine MG 1. Both the rotating electrical machines MG1 and MG2 function as electric motors and also as generators. The output shaft of the second rotating electrical machine MG2 is coupled to the drive wheels 108. The second rotating electrical machine MG2 functions mainly as an electric motor and supplies drive torque to the drive wheels 108 during running of the vehicle. The second rotating electrical machine MG2 also functions as a generator that generates electric power by braking force when the vehicle is braked. The first rotating electric machine MG1 functions mainly as a generator, and is coupled to the power split mechanism 106 to receive surplus power of the engine 104 and generate electric power. The first rotating electrical machine MG1 also functions as a starter motor for starting the engine 104. As described above, since the electric vehicle 100 disclosed in the present specification includes the engine 104, the battery 12 can be charged even during the running of the vehicle by using the surplus power of the engine 104. Further, a fuel cell or the like may be mounted instead of the engine.

The inverter (inverter)102 converts dc power into ac power and converts ac current into dc power. Specifically, the inverter 102 converts dc power supplied from a battery 12, which will be described later, into ac power, and outputs the ac power to the first rotating electrical machine MG1 and the second rotating electrical machine MG2, which are driven as electric motors. The inverter 102 converts ac power generated by the first rotating electric machine MG1 and the second rotating electric machine MG2 driven as generators into dc power and supplies the dc power to the battery 12. Further, a transformer for stepping up or stepping down the electric power may be provided between the inverter 102 and the battery 12. The driving of the inverter 102 and/or the rotary electric machines MG1, MG2, the engine 104, and the like is controlled by a control device (electronic control unit) 14.

The battery system 10 includes a rechargeable battery 12. The battery 12 is a secondary battery that supplies electric power for driving the rotating electric machines MG1, MG2 and stores electric power generated by the rotating electric machines MG1, MG 2. The battery 12 has a plurality of cells connected in series or in parallel. Various types of batteries 12 can be considered, but in this example, a lithium ion secondary battery using a composite body containing a silicon-based material and graphite as a negative electrode active material is used. When a composite containing a silicon-based material and graphite is used as the negative electrode active material, the battery 12 has a partially significant hysteresis in the change characteristic of the open circuit voltage value Vo with respect to the charging rate Cb, which will be described later. At this time, the charging rate Cb is a value (%) obtained by multiplying the current charging capacity with respect to the full charging capacity FCC Of the battery 12 by 100%, and is generally referred to as a State Of Charge (SOC).

The battery system 10 is provided with a current sensor 20, a voltage sensor 22, a temperature sensor 24, and the like for determining the state of the battery 12. The current sensor (current detector) 20 detects a current value input to and output from the battery 12. The detected current value is input to control device 14 as detected current value Ib. The voltage sensor (voltage detector) 22 detects the inter-terminal voltage value of the battery 12. The detected voltage value is input to control device 14 as detected voltage value Vb. The battery 12 is usually a battery pack in which a plurality of battery cells are connected in series or in parallel. Therefore, the voltage sensor 22 may be provided for each battery cell, or may be provided for each block including a plurality of battery cells, or only one voltage sensor 22 may be provided for the entire battery pack. The temperature sensor 24 detects the temperature of the battery 12. The detected temperature is input to the control device 14 as a battery temperature Tb. One or more temperature sensors 24 may be provided. When a plurality of voltage sensors 22 or temperature sensors 24 are provided, statistical values of the detection values of the plurality of voltage sensors 22 or temperature sensors 24, for example, an average value, a maximum value, a minimum value, and the like, may be set as the detection voltage value Vb or the battery temperature Tb.

Furthermore, the battery system 10 also has a charger 16 and a connector 18 for externally charging the battery 12. The external charging is charging of the battery 12 with electric power from an external power supply (e.g., a commercial power supply) provided outside the electric powered vehicle 100. The connector 18 can be connected to a connector (so-called charging plug) of the external power supply. The charger 16 converts external power (ac power) supplied via the connector 18 into dc power and supplies the dc power to the battery 12. Further, if the battery 12 can be charged in a state where the vehicle 100 is stopped, a charging mechanism other than a mechanism for performing external charging may be provided. For example, a solar panel or the like that generates power with sunlight may be provided in place of the charger 16 or the like for external charging or in addition to the charger 16 or the like. In some cases, a charging mechanism for charging the battery 12 in a state where the vehicle 100 is stopped may be omitted.

The control device 14 controls driving of drive sources such as the rotating electrical machines MG1, MG2, and the engine 104, and controls charging and discharging of the battery 12. The control device 14 includes a sensor interface 26, a memory 28, a CPU30, and the like.

Various sensors

20, 22, 24 are connected to the sensor interface 26. The sensor interface 26 outputs control signals to the

various sensors

20, 22, 24, and converts data input from the

various sensors

20, 22, 24 into signal forms that can be processed by the CPU 30. The memory 28 stores various control parameters and/or various programs. The CPU30 performs various information processing and/or arithmetic operations. The sensor interface 26, the CPU30, and the memory 28 are connected to each other via a data bus 44. Note that, although the control device 14 is illustrated as one block in fig. 1, the control device 14 may be configured by a plurality of devices (e.g., a plurality of CPUs 30, a plurality of memories 28, etc.). Further, a part of the functions of the control device 14 may be realized by an external device provided outside the vehicle and capable of wirelessly communicating with a control device provided in the vehicle.

The control device 14 controls charging and discharging of the battery 12 so that the charging rate Cb of the battery 12 does not exceed a predetermined upper limit value and a predetermined lower limit value. To enable such control, the control device 14 periodically estimates and monitors the charging rate Cb of the battery 12. Control device 14 estimates charging rate Cb from open-circuit voltage value Vo of battery 12 or from current integrated value Δ Ah. The current integrated value Δ Ah is an integrated value of the current input to and output from the battery 12, and is usually obtained by Σ (Ib × Δ t)/3600 when the sampling period of the detected current value Ib is Δ t. Here, when the battery is used with excessive charging, Δ Ah is on the side where the battery capacity increases (the side where the SOC increases). When the battery is used in a state of excessive discharge, Δ Ah is on the side of decreasing the battery capacity (on the side of decreasing the SOC).

Specifically describing the estimation of the charging rate Cb, the memory 28 stores the full charge capacity FCC and the SOC-OCV curve of the battery 12. The SOC-OCV curve is a curve showing a change in the open-circuit voltage value Vo with respect to the charging rate Cb of the battery 12. Fig. 2 shows an example of the SOC-OCV curve. The control device 14 estimates the charging rate Cb by comparing the open-circuit voltage value Vo of the battery 12 with the SOC-OCV curve. The open circuit voltage value Vo is the inter-terminal voltage of the battery 12 in a state where the battery 12 is not polarized (relaxed state). The open circuit voltage Vo used in the various calculations may be either an actual measured value or an estimated value. Therefore, when the charging and discharging of the battery 12 are stopped for a certain period of time and the polarization is eliminated, the detected voltage value Vb detected by the voltage sensor 22 may be set as the open-circuit voltage value Vo. When polarization occurs, if the current flowing through the battery 12 is small and the polarization component can be estimated with high accuracy, the value obtained by correcting the influence of polarization based on the detected voltage value Vb detected by the voltage sensor 22 is also treated as the open circuit voltage value Vo.

As another aspect, control device 14 calculates change amount Δ Cb of charging rate Cb from the value of current integrated value Δ Ah, and adds the previous charging rate Cb to change amount Δ Cb, thereby estimating current charging rate Cb. The change amount Δ Cb of the charging rate Cb is a ratio of the current integrated value Δ Ah to the full charge capacity FCC, and can be obtained by performing an operation of (Δ Ah/FCC) × 100.

As is clear from the above description, when estimating the state of charge Cb, the SOC-OCV curve and/or the full charge capacity FCC may be referred to. Therefore, in order to accurately estimate the current charging rate Cb, the SOC-OCV curve and/or the full charge capacity FCC stored in the memory 28 must accurately reflect the current state of the battery 12. Here, the SOC-OCV curve and/or the full charge capacity FCC gradually change with the aging degradation of the battery 12. Therefore, in order to accurately estimate the current charging rate Cb, it is desirable to estimate the aged deterioration of the battery 12 as needed, and correct and update the SOC-OCV curve and/or the full charge capacity FCC stored in the memory 28 as needed. Therefore, the control device 14 also estimates the aged deterioration of the battery 12 as needed. The estimation of the aged deterioration of the battery 12 will be described in detail below.

The aged deterioration of the battery 12 is generally estimated based on the open-circuit voltage values Vo at the plurality of separated points and the current integrated value Δ Ah between the plurality of points. However, as described above, the SOC-OCV curve of the battery 12 of the present example partially has a significant hysteresis. This is explained with reference to fig. 2. Fig. 2 is a diagram showing an example of the SOC-OCV curve of the battery 12. In fig. 2, the horizontal axis shows the charging rate cb (soc), and the vertical axis shows the open-circuit voltage value Vo. In fig. 2, the solid line is an SOC-OCV curve obtained during charging after the battery 12 is completely discharged. It can be said that the SOC-OCV curve after continuous charging. Hereinafter, this curve is referred to as "charge OCV" or "OCV _ ch". The one-dot chain line represents an SOC-OCV curve obtained during discharge after the battery 12 is fully charged. It can be said that the SOC-OCV curve after the discharge is sustained. Hereinafter, this curve is referred to as "discharge OCV" or "OCV _ dis".

As is clear from fig. 2, in the high SOC region where the charging rate Cb is relatively high, the difference between OCV _ ch and OCV _ dis is almost zero, and in this region, no significant hysteresis is present. On the other hand, in a low SOC region where charging rate Cb is relatively low, OCV _ dis and OCV _ ch have a difference of a certain value or more, and a significant lag occurs. Hereinafter, the region where no significant hysteresis occurs is referred to as a "non-hysteresis region". In addition, a region where significant hysteresis occurs is referred to as a "hysteresis region". The charging rate at the boundary between the non-hysteresis region and the hysteresis region is referred to as boundary charging rate Cb _ b. When the voltage indicated by OCV _ ch is Vch [ n ], the voltage indicated by OCV _ dis is Vdis [ n ], and the predetermined threshold is Δ Vdef when the charging rate Cb is n, the non-hysteresis region is a region satisfying (| Vch [ n ] -Vdis [ n ] | < Δ Vdef), and the hysteresis region is a region satisfying (| Vch [ n ] -Vdis [ n ] | | ≧ Δ Vdef).

In the non-hysteresis region, it can be considered that: if the value of the open-circuit voltage value Vo is the same, the value of the charging rate Cb is the same regardless of whether discharging is continued or charging is continued. In other words, it can be said that the open-circuit voltage value Vo obtained in the non-hysteresis region can uniquely represent the state of the battery 12. On the other hand, in the hysteresis region, even if the value of the open-circuit voltage value Vo is the same, the corresponding charging rate Cb is different after the continuous discharge and after the continuous charge. For example, when the open-circuit voltage value Vo is Va, the charging rate Cb is Co after the discharge is continued, and the charging rate Cb is Ci after the charge is continued. When charge and discharge are alternately repeated, even if the open-circuit voltage value Vo is Va, the charging rate Cb may be located between Co and Ci. Therefore, the open-circuit voltage value Vo obtained in the hysteresis region cannot uniquely show the state of the battery 12.

In this way, when the open circuit voltage value Vo that cannot uniquely show the state of the battery 12 is used, it is difficult to uniquely estimate the aged deterioration of the battery 12. Therefore, in order to avoid such a problem, in the battery system 10 disclosed in the present specification, in order to easily and accurately estimate the aged deterioration, the deterioration is estimated using only the open-circuit voltage value Vo and the current integrated value Δ Ah acquired in the non-hysteresis region.

Fig. 3 is a flowchart showing the most basic flow of the aged deterioration estimation process of the battery 12. The control device 14 executes the flowchart shown in fig. 3 periodically or at a certain timing (timing) to estimate the aged deterioration.

The aged deterioration estimation process is roughly divided into a parameter acquisition routine (S10) and a deterioration estimation routine (S20). In the parameter acquisition routine, in the non-hysteresis region, the first open voltage value Vo1, the second open voltage value Vo2, and the current integrated value Δ Ah12 that changes from the first open voltage value Vo1 to the second open voltage value Vo2 are acquired. The first open-circuit voltage value Vo1 and the second open-circuit voltage value Vo2 are not particularly limited if they are open-circuit voltage values Vo obtained when the charging rate Cb is in the non-hysteresis region (Cb _ b ≦ Cb ≦ 100). However, considering the accuracy of the degradation estimation of the battery 12, it is desirable that the first open voltage value Vo1 and the second open voltage value Vo2 be separated to some extent. In summary, it can be said that the first open-circuit voltage value Vo1, the second open-circuit voltage value Vo2, and the current integrated value Δ Ah12 obtained in the non-hysteresis region are parameters uniquely showing the current state of the battery 12.

In the degradation estimation routine (S20), the aged degradation of the battery 12 is estimated using the parameters acquired in the parameter acquisition routine (S10). Specifically, the control device 14 estimates at least one of the current full charge capacity FCC and the SOC-OCV curve of the battery 12 using the acquired parameters. Various forms are conceivable as the estimation method, and this will be described in detail later. In addition, when the estimation is performed in any form, the current state of the battery 12 can be accurately estimated without being affected by the hysteresis by using the parameters obtained in the non-hysteresis region.

Next, a specific example of the parameter acquisition routine will be described. Fig. 4A and 4B are flowcharts showing an example of the parameter acquisition routine. In the illustrated example of fig. 4A and 4B, the first open-circuit voltage value Vo1, the second open-circuit voltage value Vo2, and the current integrated value Δ Ah are acquired with the timing of externally charging the battery 12₁₂. In the illustrated example of fig. 4A and 4B, in order to acquire the above-described parameters, the first charging rate Cb1 and the second charging rate Cb2 are stored in the memory 28 in advance.

Both the first charging rate Cb1 and the second charging rate Cb2 have values in the non-hysteresis region and are sufficiently separated from each other (see fig. 2). The first charging rate Cb1 and the second charging rate Cb2 may be fixed values or variable values. Here, the non-hysteresis region and hence the boundary charging rate Cb _ b change with the aging deterioration of the battery 12. Therefore, when first charging rate Cb1 and second charging rate Cb2 are fixed values, first charging rate Cb1 and second charging rate Cb2 are set to values within the non-hysteresis region even if the non-hysteresis region expands and contracts with the aging degradation of battery 12. When first state of charge Cb1 and second state of charge Cb2 are set to the variable values, first state of charge Cb1 and second state of charge Cb2 may be varied in conjunction with the expansion and contraction of the non-hysteresis region associated with the aged deterioration of battery 12.

In the illustrated example of fig. 4A and 4B, as described above, in the parameter acquisition routine, the control device 14 monitors the presence or absence of an external charging instruction in order to acquire a parameter using the timing at which external charging is performed (S110). If an external charging instruction is given, control device 14 starts external charging (S112).

During execution of the external charging, the control device 14 confirms whether the charging rate Cb reaches the first charging rate Cb1 stored in the memory 28 (S114). Here, the current charging rate Cb is estimated from the open circuit voltage value Vo or the current integrated value Δ Ah, but during the external charging execution period, the open circuit voltage value Vo needs to be estimated by subtracting the polarization component from the detection voltage value Vb because the detection voltage value Vb does not contain the polarization component. However, in the low SOC region (hysteresis region), since there is an influence of hysteresis, it is difficult to uniquely determine the charging rate Cb from the open-circuit voltage value Vo without considering the past charge-discharge history. Therefore, in the hysteresis region, it is desirable to weight the current integrated value Δ Ah and estimate the charging rate Cb at a predetermined cycle regardless of the external charging period or the traveling period.

If the charging rate Cb becomes the first charging rate Cb1, the control device 14 stops the external charging (S116). During this stop period, the control device 14 checks whether or not polarization is eliminated at a predetermined cycle (S118). If the polarization is eliminated as a result of the confirmation, the control device 14 actually measures the detected voltage value Vb at that time as the first open-circuit voltage value Vo1 (S120).

If the first open voltage value Vo1 can be acquired, external charging is started again (S122). Further, the current integration value Δ Ah is started₁₂Is calculated (S124). This external charging is performed until charging rate Cb reaches second charging rate Cb2 stored in memory 28 (yes in S126). If the charging rate Cb becomes the second charging rate Cb2, the charging is stopped and stands by until the polarization is eliminated (S128). If the polarization is eliminated (yes in S130), the control device 14 actually measures the detected voltage value Vb at that time as the second open voltage value Vo2 (S132). The controller 14 acquires the current integrated value Δ Ah12 from the measured first open voltage value Vo1 to the measured second open voltage value Vo 2(S124, S133).

If the second open voltage value Vo2 can be acquired, the control device 14 starts external charging again (S134). Then, if the charging rate Cb reaches a predetermined target charging rate (for example, 90%), it is determined that the charging is completed (S136), and the external charging is ended (S138). Thereby, the parameter acquisition routine ends. Further, if the target charging rate is within the non-hysteresis region, the target charging rate may also be set to the second charging rate Cb 2. In this case, since the charging is completed in step S133, steps S134 and S136 are not required.

Fig. 5 is a diagram showing a working example of the parameter acquisition routine. In fig. 5, the horizontal axis shows time and the vertical axis shows charging rate Cb. In fig. 5, when external charging is started at time t1, charging rate Cb gradually increases. Also, if the charging rate Cb reaches the first charging rate Cb1 at time t2, the control device 14 stops the external charging. As a result, the period during which charging and discharging are not performed continues. Since this charge-discharge stop period continues, the polarization of the battery 12 is gradually eliminated. Then, if the influence of polarization disappears at time t3, control device 14 acquires detected voltage value Vb at the time point of time t3 as first open-circuit voltage value Vo 1.

If the first open voltage value Vo1 can be acquired, the control device 14 starts external charging again. By performing external charging, the charging rate Cb gradually increases. Then, if the charging rate Cb reaches the second charging rate Cb2 at time t4, the external charging is stopped again and stands by. Then, if the influence of polarization disappears at time t5, control device 14 acquires detected voltage value Vb at the time point of time t5 as second open voltage value Vo 2. The control device 14 acquires the integrated value of the detected current value Ib from time t3 to time t5 as the current integrated value Δ Ah₁₂. If the second open voltage value Vo2 is acquired, the control device 14 starts external charging again. And, if the charging rate Cb reaches the target charging rate at time t6, the external charging is stopped.

As is clear from the above description, the parameter acquisition routine can acquire the open-circuit voltage values Vo1 and Vo2 and the current integrated value Δ Ah in the non-hysteresis region₁₂. In other words, it can be said that the acquired open-circuit voltage values Vo1 and Vo2 and the current integrated value Δ Ah are obtained₁₂Is a value that is not affected by hysteresis. By estimating the deterioration with age based on this value, the deterioration with age can be estimated easily and accurately. Further, the parameter acquisition routine shown in FIG. 4A and FIG. 4B,the external charging is assumed, but if the battery 12 can be charged while the vehicle is stopped, the charging may be performed in another form. For example, the solar cell may be charged with electric power generated in the solar power generation panel.

Next, another example of the parameter acquisition routine will be described. Fig. 6 is a flowchart showing another example of the parameter acquisition routine. In the example of the graph of fig. 6, when the vehicle is driven after the external charging is completed, the first open-circuit voltage value Vo1, the second open-circuit voltage value Vo2, and the current integrated value Δ Ah are acquired with the timing at which the charging rate Cb falls₁₂. That is, in general, in electrically powered vehicle 100, in order to store the generated electric power generated by rotating electric machines MG1 and MG2 or supply electric power for driving rotating electric machines MG1 and MG2, as necessary, charging rate Cb of battery 12 is kept at intermediate value Cb _ c (for example, about 30%) which is relatively low and in the hysteresis region. Therefore, when the vehicle is driven after the external charging is completed, control device 14 decreases charging rate Cb of battery 12 to about intermediate value Cb _ c. In the graph example of fig. 6, the parameters necessary for the aged deterioration estimation are acquired at the timing when the charging rate Cb decreases from the full charge.

In the example of the graph of fig. 6, the reference current integrated value Δ Ahdef and the reference elapsed time tdef are stored in advance in order to obtain the above parameters. The flow of fig. 6 has acquired the first open voltage value Vo1 and the second open voltage value Vo2 for the purpose of performing degradation estimation, but in order to ensure the accuracy of degradation estimation, it is desirable that: the absolute value | Δ Ah of the current integrated value during the period from the acquisition of the first open-circuit voltage value Vo1 to the acquisition of the second open-circuit voltage value Vo2₁₂L is large to some extent. The reference current integrated value Δ Ahdef is an absolute value | Δ Ah of the current integrated value required for maintaining the degradation estimation accuracy₁₂The size of |. In addition, the elapsed time t from the acquisition of the first open-circuit voltage Vo1 to the acquisition of the second open-circuit voltage Vo2₁₂If the current sensor error is excessively large, the current integrated value Δ Ah is caused by the influence of the current sensor error₁₂The accumulated error component contained may become large, which may cause deterioration in the accuracy of estimation. Reference elapsed time tdef isCurrent integrated value Δ Ah₁₂The cumulative error of (2) is suppressed to a certain value or less. The reference current integrated value Δ Ahdef and the reference elapsed time tdef may be fixed values or may be variable values that vary depending on the degree of deterioration of the battery 12 and/or the current sensor 20, the ambient temperature, and the like.

The parameter acquisition routine of fig. 6 is started from the timing at which the external charging of the battery 12 is completed. If the external charging is completed, the control device 14 monitors whether the open-circuit voltage value Vo can be acquired (S140). Here, the ability to acquire the open circuit voltage value Vo includes a state in which the polarization of the battery 12 has been eliminated and the detection voltage value Vb can be directly treated as the open circuit voltage value Vo. Therefore, for example, it can be said that the open-circuit voltage value Vo can be acquired immediately after the power supply of the vehicle is turned on, so-called immediately after ignition, after the external charging is completed. The open circuit voltage value Vo includes a state in which a very small current flows through the battery 12 but the polarization component can be estimated with high accuracy. In this case, the control device 14 acquires a value obtained by correcting the influence of the estimated polarization component from the detected voltage value Vb as the open circuit voltage value Vo at that time point. Therefore, for example, it can be said that the open-circuit voltage value Vo can be acquired even during a period when the vehicle is temporarily stopped by a signal during traveling, a period when the vehicle is traveling only by the engine 104 (a period when the rotary electric machines MG1 and MG2 are not driven), or the like.

If it is determined that the open-circuit voltage value Vo can be acquired, the control device 14 checks whether the charging rate Cb at that point in time is within the non-hysteresis region (S142). The charging rate Cb in this case may be a value estimated by weighting the open-circuit voltage value Vo, or a value estimated by weighting the current integrated value Δ Ah. In the case where the charging rate Cb is not in the non-hysteresis region, the control device 14 returns to step S140. On the other hand, in the case where the charging rate Cb is in the non-hysteresis region, the control device 14 acquires the open-circuit voltage value Vo at that point in time as the first open-circuit voltage value Vo1 (S144).

If the first open-circuit voltage value Vo1 can be acquired, the control device 14 starts to perform the current flowCumulative value Δ Ah₁₂Is calculated and is compared with the elapsed time t₁₂Is counted (S146). After that, the control device 14 will pass the time t₁₂And compared with the reference elapsed time tdef (S148). At the result of the comparison is the elapsed time t₁₂When the reference elapsed time tdef is exceeded (no in S148), the control device 14 determines that the current integration error is greater than or equal to a certain value. In this case, the control device 14 returns to step S140 and resumes the acquisition of the first open voltage value Vo 1. On the other hand, at the elapsed time t₁₂When the reference elapsed time tdef is equal to or less than the reference elapsed time (yes in S148), the control device 14 then sets the current integrated value Δ Ah to the current integrated value Δ Ah₁₂And is compared with the reference current integrated value Δ Ahdef (S150). If the result of the comparison is | Δ Ah₁₂If | is less than Δ Ahdef (no in S150), the process returns to step S148. On the other hand, if the result of the comparison is | Δ Ah₁₂If | ≧ Δ Ahdef (yes in S150), control device 14 confirms whether or not open-circuit voltage value Vo can be acquired, and also confirms whether or not current state of charge Cb is in the no-lag region (S152, S154). If at least one of the conditions is not satisfied as a result of the confirmation (no in S152, no in S154), the control device returns to step S148. On the other hand, if the open circuit voltage value Vo can be acquired and the charging rate Cb is within the non-hysteresis region (yes in S152 and yes in S154), the control device 14 acquires the open circuit voltage value Vo at that point in time as the second open circuit voltage value Vo2 (S156).

If the second open-circuit voltage value Vo2 can be acquired, the control device 14 ends the current integrated value Δ Ah at that point in time₁₂Is calculated and is compared with the elapsed time t₁₂Is counted (S158). And, thereby, the parameter acquisition routine ends. In the example of fig. 6, the current integrated value Δ Ah is monitored when the second open-circuit voltage value Vo2 is acquired₁₂And elapsed time t₁₂But these may also be omitted. That is, in fig. 6, steps S148 and S150 may be omitted.

Fig. 7 is a diagram showing a working example of the parameter acquisition routine. In fig. 7, the horizontal axis shows time and the vertical axis shows charging rate Cb. In the example of fig. 7, the reference elapsed time tdef ratio is from the time t1 to the time t5The time of stopping is large enough. The working example of fig. 7 starts from a state where the external charging of the battery 12 is completed and the charging rate Cb of the battery 12 is close to the full charge (e.g., 90%, etc.). When the power of electrically powered vehicle 100 is turned on at time t1, control device 14 starts the routine of fig. 6. It can be said that immediately after the power is turned on, the polarization state of the battery 12 is eliminated, and the open circuit voltage value Vo can be obtained. Therefore, the control device 14 acquires the detected voltage value Vb immediately after the power is turned on, that is, at time t1, as the first open-circuit voltage value Vo 1. Further, the control device 14 starts calculating the current integrated value Δ Ah12 and starts calculating the elapsed time t₁₂Is counted.

Then, the control device 14 controls the charging and discharging of the battery 12 so that the excessive discharging (for example, EV running) is performed until the charging rate Cb reaches a predetermined intermediate value Cb _ c (for example, about 30%). Here, it is assumed that: during the period from time t2 to time t3, the vehicle is stopped by a signal, for example, and the state where the charge/discharge amount of the battery 12 is reduced and the load is small continues. In this case, the open-circuit voltage value Vo at time t3 can be obtained by removing the estimated polarization component from the detected voltage value Vb. However, at time t3, the absolute value | Δ Ah of the current integrated value₁₂Since | is smaller than the reference current integrated value Δ Ahdef, the control device 14 continues the process of acquiring the second open voltage value Vo 2.

Then, the following steps are performed: during the period from time t4 to time t5, the vehicle is stopped again by a signal, for example, and the state where the charge/discharge amount of the battery 12 is reduced and the load is small continues. In this case, the open-circuit voltage value Vo at time t5 can be obtained by removing the estimated polarization component from the detected voltage value Vb. In addition, it is assumed that: at time t5, the absolute value | Δ Ah12| of the current integrated value is larger than the reference current integrated value Δ Ahdef, the elapsed time t12 is smaller than the reference elapsed time tdef, and the charging rate Cb is in the no-lag region. In this case, the control device 14 acquires the open voltage value Vo at time t5 as the second open voltage value Vo2, and ends the parameter acquisition routine.

As is clear from the above description, in the parameter acquisition routine shown in fig. 6, the first open-circuit voltage value Vo1, the second open-circuit voltage value Vo2, and the current integrated value Δ Ah12 are also acquired in the non-hysteresis region. In other words, it can be said that the acquired open-circuit voltage values Vo1, Vo2 and the current integrated value Δ Ah12 are values not affected by hysteresis. By estimating the aged deterioration based on this value, the aged deterioration can be estimated easily and accurately.

Next, another example of the parameter acquisition routine will be explained with reference to fig. 8A and 8B. Fig. 8A and 8B are flowcharts showing another example of the parameter acquisition routine. In the graph examples of fig. 8A and 8B, the timing of parameter acquisition is forcibly generated by controlling the charge and discharge of the battery 12. That is, as described above, in electric powered vehicle 100, normally, the charging rate Cb of battery 12 is kept at intermediate value Cb _ c (for example, about 30%) which is relatively low and is in the hysteresis region. If this state continues for a long time, the parameters used for estimating the aged deterioration cannot be acquired. Therefore, if the elapsed time te since the previous annual degradation estimation process was performed is equal to or longer than the predetermined reference time t _ def2, the control device 14 forcibly increases the charging rate Cb of the battery 12 to the non-hysteresis region, and acquires the parameter necessary for estimating the annual degradation. The value of the reference time t _ def2 is not particularly limited, and is, for example, several weeks to several months, because it depends on the deterioration rate of the battery.

In addition, in the graph examples of fig. 8A and 8B, in order to acquire the parameters, the first charging rate Cb1 and the second charging rate Cb2 are stored in advance in the memory 28. The first charging rate Cb1 and the second charging rate Cb2 are substantially the same as the first charging rate Cb1 and the second charging rate Cb2 described in the routines of fig. 4A and 4B, and may be either fixed values or variable values if they are in the non-hysteresis region.

In order to execute the parameter acquisition routine, control device 14 has a normal mode, an overcharge mode, and a charge-discharge limit mode as control modes of electric powered vehicle 100. The overcharge mode is a control mode in which the charge amount of the battery 12 is larger than the discharge amount. For example, in the overcharge mode, the control device 14 drives the engine 104 so that the engine 104 outputs power equal to or higher than power required for running of the vehicle, and causes the first rotating electrical machine MG1 to generate electric power by the surplus power of the engine 104. At this time, the control device 14 permits only the second rotating electrical machine MG2 to generate electric power using the braking force, and prohibits the second rotating electrical machine MG2 from being driven as an electric motor.

The charge/discharge limitation mode is a mode in which both the charge and discharge of the battery 12 are limited. For example, in the charge/discharge limitation mode, the control device 14 controls the engine 104 so that the engine 104 outputs the power required for the traveling of the vehicle, and limits the driving of the first rotating electric machine MG1 and the second rotating electric machine MG2 as much as possible. That is, the power generation by the first rotating electrical machine MG1 and the second rotating electrical machine MG2 is also restricted. The normal mode means a control mode that is not either the overcharge mode or the charge-discharge limit mode, and may be an electric drive running in which the vehicle is run by the power of only the second rotating electric machine MG2 or a hybrid drive running in which the vehicle is run by the power of the second rotating electric machine MG2 and the engine 104, as necessary.

In the parameter acquisition routine of fig. 8A and 8B, the control device 14 counts the elapsed time te since the previous aged deterioration estimation process was performed, and monitors whether or not the elapsed time te is equal to or longer than a predetermined reference time t _ def2 (S160). If the elapsed time te is equal to or longer than the reference time t _ def2, the control device 14 switches the control mode of the vehicle to the overcharge mode (S162). Thereby, the charging rate Cb of the battery 12 gradually increases from the intermediate value Cb _ c (for example, about 30%) in the hysteresis region to reach the non-hysteresis region.

If the charging rate Cb of the battery 12 is the first charging rate Cb1 that is a value in the non-hysteresis region (yes in S164), the control device 14 switches the control mode of the vehicle to the charge-discharge limiting mode in which both the charge and the discharge are limited (S166). This restricts the charge and discharge of the battery 12, and facilitates acquisition of the open-circuit voltage value Vo. Then, if the open circuit voltage value Vo can be acquired (yes in S168), the control device 14 acquires the open circuit voltage value Vo at that point in time as the first open circuit voltage value Vo1 (S170).

If the first open voltage value Vo1 can be acquired, the control device 14 switches the control mode of the electric vehicle 100 to the overcharge mode again (S172). Further, the control device 14 starts the calculation of the current integrated value Δ Ah12 (S174).

As a result of switching to the overcharge mode, the charging rate Cb of the battery 12 starts to rise again. And, if the charging rate Cb of the battery 12 becomes the second charging rate Cb2 (yes in S178), the control device 14 switches the control mode to the charge-discharge limiting mode again (S180). Then, if the open circuit voltage value Vo can be acquired (yes in S182), the control device 14 acquires the open circuit voltage value Vo at that point in time as the second open circuit voltage value Vo2 (S184). In addition, if the second open-circuit voltage value Vo2 can be acquired, the control device 14 ends the current integrated value Δ Ah₁₂Is calculated (S186). If the first open-circuit voltage Vo1, the second open-circuit voltage Vo2 and the integrated current value Δ Ah can be obtained₁₂Then, the control device 14 switches the control mode of the motor vehicle 100 to the normal mode (S188). In addition, the absolute value | Δ Ah of the current integrated value₁₂If | is smaller than the predetermined reference value, the deterioration estimation accuracy may be reduced. Therefore, it is preferable to control the absolute value | Δ Ah12| of the current integrated value to be equal to or greater than a predetermined reference value. In this example, as in the flowchart of fig. 6, the elapsed time t from the acquisition of the first open-circuit voltage value Vo1 may be checked immediately before the acquisition of the second open-circuit voltage value Vo2₁₂. In this case, at the elapsed time t₁₂When the voltage exceeds the predetermined reference value, the second open voltage Vo2 is not acquired, and after the operation in the overdischarge mode, the process returns to step S164 to acquire the first open voltage Vo1 again.

Fig. 9 is a diagram showing a working example of the parameter acquisition routine. In fig. 9, the horizontal axis shows the time and the vertical axis shows the charging rate Cb. The operation example of fig. 9 starts from a state where the charging rate Cb of the battery 12 is maintained at about the intermediate value Cb _ c in the hysteresis region. Normally, the charging rate Cb of the battery 12 is held around the intermediate value Cb _ c. Now, at time t1, the elapsed time te since the previous annual degradation estimation process has reached the reference time t _ def2 or more. In this case, the control device 14 switches the control mode of the vehicle to the overcharge mode. As a result, the charging rate Cb of the battery 12 rises. Then, at time t2, charging rate Cb is assumed to be first charging rate Cb 1. In this case, the control device 14 switches to the charge/discharge limiting mode. As a result, after time t2, the variation in the charging rate Cb becomes small. If the open-circuit voltage value Vo can be acquired at time t3 when this state continues for a certain period, the control device 14 acquires the open-circuit voltage value Vo at time t3 as the first open-circuit voltage value Vo 1.

If the first open-circuit voltage value Vo1 can be acquired, the control device 14 switches to the overcharge mode again. Further, the calculation of the current integrated value Δ Ah12 is also started. As a result, the charging rate Cb of the battery 12 rises sharply after the time t 3. Also, if the charging rate Cb becomes the second charging rate Cb2 at time t4, the control device 14 switches to the charge-discharge limiting mode again. At time t5 when the charge/discharge restricted state continues for a fixed period, the open-circuit voltage value Vo can be obtained. The control device 14 acquires the open-circuit voltage value Vo at the time t5 as the second open-circuit voltage value Vo 2. The integrated value of the detected current value Ib from time t3 to time t5 is acquired as the current integrated value Δ Ah 12. Then, if the first open voltage value Vo1, the second open voltage value Vo2, and the current integrated value Δ Ah12 can be obtained, the control device 14 switches the control mode of the hybrid vehicle to the normal mode. As a result, the charging rate Cb of the battery 12 decreases toward the intermediate value Cb _ c.

As is clear from the above description, in the parameter acquisition routine shown in fig. 8A and 8B, the first open-circuit voltage value Vo1, the second open-circuit voltage value Vo2, and the current integrated value Δ Ah12 are also acquired in the non-hysteresis region. In other words, it can be said that the acquired first open-circuit voltage value Vo1, second open-circuit voltage value Vo2, and current integrated value Δ Ah12 are values not affected by hysteresis. By estimating the aged deterioration based on this value, the aged deterioration can be estimated easily and accurately.

In addition, if the aged deterioration is not estimated for a long period of time, the difference between the actual state of the battery 12 and the SOC-OCV curve and the full charge capacity FCC stored in the memory 28 becomes large. In this case, the estimation accuracy of the state of charge Cb of the battery 12 is lowered. As shown in the routines shown in fig. 8A and 8B, even when external charging or the like is not performed for a long period of time, if the elapsed time te from the previous aged deterioration estimation process becomes equal to or longer than the reference time t _ def2, the parameters necessary for aged deterioration can be acquired. Therefore, it is possible to avoid a problem that the estimation accuracy of SOC is lowered due to long-term non-estimation of aged deterioration. Further, in the example of fig. 8A and 8B, Cb1 < Cb2 is assumed, and the first open voltage value Vo1 acquired at the first time is lower than the second open voltage value Vo2 acquired at the second time. However, Cb1 > Cb2 may be set so that the first open-circuit voltage value Vo1 is acquired by first charging before the charging rate Cb reaches the first charging rate Cb1, and then the operation is performed so as to discharge the excessive charge, and the second open-circuit voltage value Vo2 is acquired when the charging rate Cb reaches the second charging rate Cb2 (< Cb 1).

Further, the routines shown in fig. 8A and 8B are premised on the battery 12 being able to be charged during travel of the vehicle. Therefore, the routines shown in fig. 8A and 8B are applicable to an electric vehicle capable of generating power also during traveling of the vehicle. As the electric vehicle, a hybrid vehicle having an engine as a power source in addition to a rotating electric machine, an electric vehicle having a solar panel that generates electricity by sunlight, an electric vehicle equipped with a fuel cell that converts chemical energy of fuel (hydrogen gas or the like) into electric power, and the like are in demand.

Next, the deterioration estimation routine (S20) will be described. In the degradation estimation routine (S20), if at least one of the SOC-OCV curve and the full charge capacity FCC of the battery 12 is estimated using the first open voltage value Vo1, the second open voltage value Vo2, and the current integrated value Δ Ah12 acquired in the parameter acquisition routine (S10), the form thereof is not particularly limited. Hereinafter, two types of deterioration estimation routines (S20) are exemplified, but the deterioration estimation routine (S20) is not limited to the above two types, and various conventionally proposed deterioration estimation techniques can be used.

An example of the degradation estimation routine (S20) will be described with reference to fig. 10. The degradation estimation routine of fig. 10 is based on the amount of change Δ Cb in the charging rate and the current integrated value Δ aThe ratio of h12 to estimate the full charge capacity FCC. Specifically, the control device 14 compares the first open-circuit voltage value Vo1 and the second open-circuit voltage value Vo2 acquired in the parameter acquisition routine (S10) with the SOC-OCV curve stored in the memory 28 to acquire the corresponding charging rate Cb [ Vo1 ]]、Cb[Vo2](S210, S212). Next, the controller 14 calculates the absolute value | Δ Ah of the current integrated value₁₂| Cb [ Vo1 ] by the change Δ Cb of the charging rate]－Cb[Vo2]The value obtained by multiplying the value obtained by | by 100 is defined as the full charge capacity FCC (S214). That is, FCC, | Δ Ah12|/(| Cb [ Vo 1) was performed]－Cb[Vo2]|)) × 100. Then, if the full charge capacity FCC can be calculated, the control device 14 corrects the full charge capacity FCC stored in the memory 28 and updates the corrected full charge capacity FCC to the calculated full charge capacity FCC (S216).

Next, another example of the degradation estimation routine (S20) will be described. The degradation estimation routine of fig. 11 is based on the first open voltage value Vo1, the second open voltage value Vo2, and the current integrated value Δ Ah acquired in the parameter acquisition routine₁₂Searching for three degradation parameters k representing the state of the battery 12₁、k₂、ΔQ_s. Before explaining the flow of the degradation estimation routine, the principle of the degradation estimation routine will be explained.

As described above, the battery 12 in this example is a lithium ion secondary battery composed of a negative electrode, a separator containing an electrolyte, and a positive electrode. The negative electrode and the positive electrode are each composed of an aggregate of spherical active materials. During discharge of the lithium ion secondary battery, lithium ion Li is released at the interface of the active material of the negative electrode⁺And an electron e^-The chemical reaction of (1). On the other hand, the lithium ion Li is absorbed at the interface of the active material of the positive electrode⁺And an electron e^-The chemical reaction of (1). During charging of the lithium ion secondary battery, a reaction opposite to the above reaction proceeds.

A negative electrode current collector that absorbs electrons is provided on the negative electrode, and a positive electrode current collector that emits electrons is provided on the positive electrode. The negative electrode current collector is formed of, for example, copper, and is connected to the negative electrode terminal. The positive electrode current collector is formed of, for example, aluminum, and is connected to the positive electrode terminal. The lithium ion secondary battery is charged and discharged by transferring lithium ions between the positive electrode and the negative electrode through the separator.

Here, the internal state of charge of the lithium ion secondary battery differs depending on the lithium concentration distribution in the active materials of the positive electrode and the negative electrode, respectively. The output voltage of the lithium ion secondary battery is represented by the following formula (1).

V＝Vo(θ₁，θ₂)－R×I (1)

Here, R is the resistance of the entire lithium ion secondary battery, and I is the current flowing through the lithium ion secondary battery. The resistance R includes a pure resistance that allows the negative electrode and the positive electrode to move with respect to electrons, and a charge transfer resistance that equivalently functions as a resistance when a reaction current occurs at the active material interface.

θ₁Is a local charging rate on the surface of the positive electrode active material, theta₂Is a local charging rate on the surface of the negative electrode active material. The resistance R has a value according to theta₁、θ₂And the characteristics of the battery that change with a change in temperature. In other words, the resistance R may be taken as θ₁、θ₂And battery temperature. Local charging rate theta₁、θ₂Represented by the following formula (2).

θ_i＝(C_se，i)/(C_s，i，max) (2)

Here, C_se，iIs the lithium concentration (average value) at the interface of the active material (positive electrode or negative electrode), C_s，i，maxIs the limiting lithium concentration in the active material (positive or negative). The subscript i is 1 for a positive electrode and 2 for a negative electrode. The so-called limit lithium concentration is an upper limit value of the lithium concentration at the positive electrode and/or the negative electrode. Local charging rates θ of positive and negative electrodes₁、θ₂Varying between 0 and 1, respectively.

Positive open circuit potential U₁Having a local charging rate theta according to the surface of the positive electrode active material₁And the characteristic of the change, the negative open-circuit potential U₂Having a local charging rate theta according to the surface of the negative electrode active material₂But varying characteristics. In FIG. 12, lithium ion is shownPositive open-circuit potential U of secondary battery in initial state₁With respect to local charging rate theta₁And negative open circuit potential U₂With respect to local charging rate theta₂The relationship (2) of (c). In addition, since the battery 12 of the present example uses a composite containing a silicon-based material and graphite as the negative electrode active material, the negative electrode open circuit potential U₂Partly with hysteresis. In FIG. 12, the negative open circuit potential U of the thick line₂The negative open-circuit potential U of the thin wire and the negative open-circuit potential U of the negative electrode obtained in the process of charging the battery 12 after the battery is completely discharged (hereinafter referred to as "after continuous charging") are shown₂The negative open-circuit potential obtained in the process of performing discharge after full charge (hereinafter referred to as "after continuous discharge") is shown. Similarly, the open-circuit voltage value Vo of the thick line shows the open-circuit voltage after the continuous charging, and the open-circuit voltage value Vo of the thin line shows the open-circuit voltage after the continuous discharging. Hereinafter, when there is no need to distinguish between them, only the negative electrode open circuit potential U after the continuous charging is applied₂The open circuit voltage Vo will be described.

As shown in FIG. 12, the open-circuit voltage value Vo of the lithium ion secondary battery is used as the positive electrode open-circuit potential U₁Open circuit potential U with negative electrode₂Is represented by the potential difference of (a). As described above, since the negative open circuit potential U2 has a partially lagging relationship, the open circuit voltage value Vo also has a partially lagging relationship. The initial state refers to a state in which the lithium ion secondary battery is not deteriorated, and refers to a state immediately after the lithium ion secondary battery is manufactured, for example.

As shown in fig. 12, the local charging rate θ of the positive electrode₁Is theta_1H(═ 1), positive open circuit potential U₁Lowest (maximum amount of Li in the positive electrode). On the other hand, the local charging rate θ 2 of the negative electrode is θ_2L(═ 0), the negative electrode open potential was the highest (the amount of Li in the negative electrode was the smallest). Shows the above characteristics (U)₁，U₂) The data of (2) may be stored in the memory 28 as a map in advance.

The open circuit voltage value Vo of the lithium ion secondary battery has a characteristic of decreasing from a fully charged state as discharge proceeds. In addition, in the deteriorated lithium ion secondary battery, the voltage drop amount with respect to the same discharge time becomes larger than that in the lithium ion secondary battery in the initial state. This indicates that: the deterioration of the lithium ion secondary battery causes a decrease in the full charge capacity and a change in the open circuit voltage curve. In the present embodiment, the change in the open circuit voltage curve associated with the deterioration of the lithium ion secondary battery is modeled as 2 phenomena that are considered to occur inside the lithium ion secondary battery in a deteriorated state. The 2 phenomena are a reduction in unipolar capacity at the positive and negative electrodes and a corresponding deviation in composition between the positive and negative electrodes.

The decrease in the unipolar capacity indicates a decrease in the lithium-accepting ability of each of the positive electrode and the negative electrode. The decrease in lithium-accepting ability means that active materials and the like that effectively function in charge and discharge are decreasing.

FIG. 13 schematically shows the positive open-circuit potential U due to the decrease in the positive electrode capacity₁Change of (3) and negative open circuit potential U due to decrease of negative electrode capacity₂A change in (c). In FIG. 13, Q on the axis of the positive electrode capacity_1LIs a partial charging rate theta in an initial state of the lithium ion secondary battery and fig. 12_1L(0) corresponding capacity. Q_1H＿iniIs a partial charging rate theta in an initial state of the lithium ion secondary battery and fig. 12_1H(1) corresponding capacity. In addition, on-axis Q of negative electrode capacity_2LIs a partial charging rate theta in an initial state of the lithium ion secondary battery and fig. 12_2H(1) capacity, Q_2H＿iniIs a partial charging rate theta in an initial state of the lithium ion secondary battery and fig. 12_2L(0) corresponding capacity.

In the positive electrode, when the lithium-receiving ability is lowered, the local charging rate θ_1L(1) capacity corresponding to Q_1H＿iniChange to Q_1H＿aft. In addition, in the negative electrode, when the lithium-accepting ability is lowered, the local charging rate θ is related to_2L(0) corresponds to a capacity from Q_2H＿iniChange to Q_2H＿aft。

Here, even if the lithium ion secondary battery is deteriorated, the positive electrode open circuit potential U₁With respect to local chargingRate theta₁Does not change (the relationship shown in fig. 12). Therefore, if the positive electrode is opened to the potential U₁With respect to local charging rate theta₁Is converted into a positive open-circuit potential U₁The relationship between the positive electrode capacity and the positive electrode open circuit potential U is shown in FIG. 13_1＿aftThe curve (two-dot chain line) of the relationship of the positive electrode capacity with respect to the deterioration state becomes the curve U with respect to the initial state_1＿iniThe state after the degradation of the lithium ion secondary battery occurred was contracted (solid line).

Similarly, if the negative electrode is set to the open circuit potential U₂With respect to local charging rate theta₂Is converted into a negative open-circuit potential U₂The relationship with respect to the negative electrode capacity is shown in FIG. 13, which shows the negative electrode open circuit potential U_2＿aftThe curve (two-dot chain line) of the relationship of the negative electrode capacity with respect to the deterioration state becomes the curve U with respect to the initial state_2＿iniThe state after the degradation of the lithium ion secondary battery occurred was contracted (solid line).

Next, the composition deviation will be described. The deviation of the composition correspondence between the positive electrode and the negative electrode is schematically shown in fig. 14. The deviation from compositional correspondence indicates: composition (theta) of positive electrode when charging and discharging using a combination of positive and negative electrodes₁) Composition with negative electrode (theta)₂) The combination of (a) deviates from the initial state of the lithium ion secondary battery.

Showing the open circuit potential U of the anode and cathode₁、U₂Local charging rate theta with respect to positive electrode and negative electrode₁、θ₂The curve of the relationship (c) is the same as the curve shown in fig. 12. Here, if the lithium ion secondary battery is deteriorated, the negative electrode composition θ₂Axial positive electrode composition of (a)₁Reduced directional offset delta theta₂. Thus, the negative open circuit potential U is shown_2＿aftComposition of negative electrode with respect to deterioration state θ₂Is in relation to the axis of (a two-dot chain line), with respect to a curve showing the negative open-circuit potential U_2＿iniComposition of negative electrode with respect to initial state θ₂Curve (solid line) of the relationship of axis (d), positive electrode composition θ₁Reduced direction deviation and delta theta₂In an equivalent amount.

As a result, the composition θ with the positive electrode_1fixThe composition of the corresponding negative electrode is "θ" when the lithium ion secondary battery is in an initial state_{2fix＿ini”}And becomes "θ" after the lithium ion secondary battery is deteriorated_2fix＿aft”。

In the degradation estimation routine shown in fig. 11, the above-described 2 degradation phenomena are modularized by introducing 3 degradation parameters into the battery module. The 3 deterioration parameters are the positive electrode capacity maintenance rate k₁And a negative electrode capacity retention rate k₂And the corresponding deviation capacity delta Q of the positive and negative electrode compositions_s. The following description will be made regarding a method of modularizing 2 degradation phenomena.

So-called positive electrode capacity maintenance ratio k₁Is a ratio of the positive electrode capacity in the deteriorated state to the positive electrode capacity in the initial state. Here, the positive electrode capacity is reduced by an arbitrary amount from the capacity in the initial state after the lithium ion secondary battery becomes in a deteriorated state. At this time, the positive electrode capacity retention rate k₁Represented by the following formula (3).

Here, Q_1＿iniShows the positive electrode capacity, Δ Q, of the lithium ion secondary battery in the initial state₁This shows the amount of decrease in the positive electrode capacity when the lithium ion secondary battery is deteriorated. Therefore, the positive electrode capacity when the lithium ion secondary battery is in a deteriorated state is (Q)_1＿ini－ΔQ₁). In addition, k₁Starting from 1 in the initial state and dropping. Here, the positive electrode capacity Q in the initial state_1＿iniCan be determined in advance from the theoretical capacity of the active material, the amount of the material to be prepared, and the like.

So-called negative electrode capacity retention rate k₂It is a ratio of the negative electrode capacity in the deteriorated state to the negative electrode capacity in the initial state. Here, the negative electrode capacity is reduced by an arbitrary amount from the capacity in the initial state after the lithium ion secondary battery becomes in a deteriorated state. At this timeNegative electrode capacity maintenance ratio k₂Represented by the following formula (4).

Here, Q_2＿iniShows the negative electrode capacity, Δ Q, of the lithium ion secondary battery in the initial state₂This shows the amount of decrease in the negative electrode capacity when the lithium ion secondary battery is deteriorated. Therefore, the negative electrode capacity when the lithium ion secondary battery is in a deteriorated state is (Q)_2＿ini－ΔQ₂). In addition, k₂Starting from 1 in the initial state and dropping. Here, the negative electrode capacity Q in the initial state_2＿iniCan be determined in advance from the theoretical capacity of the active material, the amount of the material to be prepared, and the like.

Fig. 15 is a schematic diagram illustrating a deviation in the composition correspondence between the positive electrode and the negative electrode. When the lithium ion secondary battery is in a deteriorated state, the composition theta with the negative electrode₂A negative electrode capacity of (Q) corresponding to 1_2＿ini－ΔQ₂). In addition, the corresponding deviation capacity DeltaQ of the positive and negative electrode compositions_sIs composed of an axis theta with the negative electrode₂Relative to the positive electrode composition axis theta₁Deviation amount Δ θ of₂The corresponding capacity. Thereby, the relationship of the following expression (5) is established. In addition, the corresponding deviation capacity Δ Q of the positive and negative electrode compositions_sThe amount of change in battery capacity due to a change in the correspondence relationship between the local state of charge θ 1, which is the local state of charge on the surface of the positive electrode active material, and the local state of charge θ 2, which is the local state of charge on the surface of the negative electrode active material, is shown.

Δθ₂：1＝ΔQ_s：(Q_2＿ini－ΔQ₂) (5)

Then, the following equation (6) is obtained from the equations (4) and (5).

ΔQ_s＝k₂×Q_2＿ini×Δθ₂ (6)

Positive electrode composition theta at the time of initial state of the lithium ion secondary battery_1fixWith the negative electrode composition theta_2fix＿iniAnd (7) corresponding. When the lithium ion secondary battery is in a deteriorated state,positive electrode composition theta_1fixWith the negative electrode composition theta_2fix＿aftAnd (7) corresponding.

When a deviation in the composition correspondence between the positive electrode and the negative electrode occurs due to deterioration of the lithium ion secondary battery, the negative electrode composition θ after deterioration of the lithium ion secondary battery_2fix＿aftHas the following relationship (7).

The meaning of formula (7) will be explained. When the lithium ion secondary battery is in a deteriorated state and lithium is released from the positive electrode by charging, the positive electrode composition θ₁Starting with 1 and decreasing. Composition at positive electrode theta₁From 1 to theta_1fixThe amount of lithium released from the positive electrode F1 is represented by the following formula (8).

F1＝(1－θ_1fix)×k₁×Q_1＿ini (8)

Here, (1-theta)_1fix) The value of (b) represents the decrease in the positive electrode composition θ 1 of the lithium ion secondary battery due to charging, (k1 × Q)_1＿ini) The value of (b) represents the positive electrode capacity after the lithium ion secondary battery is deteriorated.

When all the lithium released from the positive electrode is obtained by the negative electrode, the negative electrode composition θ_2fix＿iniThe following formula (9) is obtained.

Here, (k)₂×Q_2＿ini) The value of (b) represents the negative electrode capacity after the lithium ion secondary battery is deteriorated.

On the other hand, there is a deviation (Δ θ) in the composition correspondence between the positive electrode and the negative electrode₂) Time, deteriorated anode composition θ_2fix＿aftThis is represented by the following formula (10).

Deviation amount Delta theta corresponding to composition₂The corresponding deviation capacity DeltaQ of the positive and negative electrode composition can be obtained by the formula (6)_sTo indicate. Thereby, the deteriorated negative electrode composition θ_2fix＿aftIs represented by the above formula (7).

As shown in fig. 15, the open-circuit voltage Vo when the lithium-ion secondary battery is in the degraded state is defined as the positive-electrode open-circuit potential U in the degraded state_1＿aftOpen circuit potential U with negative electrode_2＿aftIs represented by the potential difference of (a). That is, if the positive electrode capacity maintenance rate k as the 3 degradation parameters is determined₁And a negative electrode capacity retention rate k₂Positive and negative pole composition corresponding deviation capacity delta Q_sThen, the negative electrode open circuit potential U when the lithium ion secondary battery is in a deteriorated state can be determined_2＿aftThe open-circuit voltage Vo can be calculated as the negative open-circuit potential U_2＿aftAnd positive open circuit potential U_1＿iniThe potential difference of (a).

That is, the positive electrode capacity Q in the initial state_1＿iniAnd negative electrode capacity Q_2＿iniSince the capacity can be determined in advance from the theoretical capacity and/or the amount of the active material, the positive electrode capacity retention ratio k is a deterioration parameter of 3₁And a negative electrode capacity retention rate k₂And the corresponding deviation capacity delta Q of the positive and negative electrode compositions_sIf it can be determined, the deterioration state of the negative electrode composition θ can be calculated using the formula (7)_2fix＿aft. In addition, the deviation amount Δ θ corresponding to the composition can be calculated using equation (6)₂. Therefore, as shown in fig. 12, the positive electrode composition θ associated with the deterioration state can be determined₁Negative electrode composition axis theta of deterioration state corresponding to position of 1₂Position of 0 and negative electrode composition θ_2fix＿aft. And can be based on 0 and theta_2fix＿aftDetermining the anode composition axis theta of the deteriorated state as shown in fig. 12₂Is the position of 1.

Even if the lithium ion secondary battery is deteriorated, the positive electrode has an open circuit potential U₁Local charging rate theta with respect to the positive electrode₁Relation of (1), negative open circuit potential U₂Local charging rate theta with respect to the negative electrode₂Does not change (the relationship shown in fig. 12). Therefore, if and degradationPositive electrode composition of state θ₁Negative electrode composition axis θ of deterioration state corresponding to positions of 1 and 0₂The positions of 0 and 1 can be determined, then the positive electrode composition θ in the deteriorated state₁The positive open-circuit potential U shown in FIG. 12 is plotted between 1 and 0₁Local charging rate theta with respect to the positive electrode₁Curve of relationship (c), positive electrode composition in deteriorated state θ₁The negative open-circuit potential U shown in FIG. 12 is plotted between 1 and 0₂Local charging rate theta with respect to the negative electrode₂In the case of the curves of (1), each curve represents the positive open-circuit potential U in the deteriorated state shown in FIG. 12₁And negative open circuit potential U₂. Thus, if it represents the positive open-circuit potential U₁Negative open circuit potential U₂If the curve of (b) can be determined, the open circuit voltage value Vo of the lithium ion secondary battery in a deteriorated state can be calculated.

As described above, when the positive electrode capacity retention rate k1, the negative electrode capacity retention rate k2, and the positive-negative electrode composition-based off capacity Δ Q, which are the 3 degradation parameters, were determined_sThe open circuit voltage value Vo of the lithium ion secondary battery in the deteriorated state can be calculated.

In the lithium ion secondary battery in the initial state, the positive electrode capacity retention rate k1 and the negative electrode capacity retention rate k2 were 1, and the positive and negative electrode composition-dependent off capacity Δ Q was set to 1_sAt 0, the open-circuit voltage value Vo calculated (estimated) in the above description coincides with the value (actually measured value) when the open-circuit voltage value Vo of the lithium ion secondary battery in the initial state (new product) is measured.

As shown in fig. 16, the open circuit voltage value Vo of the lithium ion secondary battery increases as the battery capacity (Δ Ah) increases, that is, as the secondary battery is charged. Hereinafter, a change curve of the open circuit voltage value Vo with respect to the battery capacity (Δ Ah) is referred to as an open circuit voltage curve. As shown by the one-dot chain line and the broken line in fig. 16, the open circuit voltage curve deviates from the initial state to the left in the figure when the battery 12 deteriorates.

As described above, the positive electrode capacity maintenance rate k can be obtained from 3 degradation parameters₁And a negative electrode capacity retention rate k₂And positive and negative electrode compositionsCorresponding deviation capacity Δ Q_sSince the open-circuit voltage value Vo of the lithium ion secondary battery in a deteriorated state is calculated, the off-capacity Δ Q can be determined according to the positive electrode capacity retention rate k1, the negative electrode capacity retention rate k2, and the positive and negative electrode composition_sAn open circuit voltage curve of the lithium ion secondary battery was calculated.

Therefore, in the degradation estimation routine shown in fig. 11, the following convergence calculation is performed: the open circuit voltage curve (estimated value) of the degradation state calculated based on the positive electrode capacity maintenance rate k1, the negative electrode capacity maintenance rate k2, and the positive/negative electrode composition deviation capacity Δ Qs as the 3 degradation parameters and the open circuit voltage curve (actual measurement value) are searched for to approximately match (k is the actual measurement value)₁，k₂，ΔQ_s) The value of (c). Thus, the positive electrode capacity retention rate k1, the negative electrode capacity retention rate k2, and the positive-negative electrode composition-corresponding offset capacity Δ Q in a certain deterioration state can be specified_sThe capacity deterioration of the lithium ion secondary battery can be estimated.

Specifically, the flow of the degradation estimation routine will be described with reference to fig. 11. In the degradation estimation routine shown in fig. 11, the controller 14 first plots the first open voltage value Vo1, the second open voltage value Vo2, and the current integrated value Δ Ah acquired in the parameter acquisition routine (S10)₁₂An open circuit voltage curve (measured value) is generated (S220).

Next, the control device 14 sets a degradation parameter (k) for generating an open-circuit voltage characteristic (estimated value)₁，k₂，ΔQ_s) The candidate value of (S222). Next, an open circuit voltage curve (estimated value) is generated using the set degradation parameter (S224). The principle of this generation is as described with reference to fig. 12 to 15. Fig. 16 is a diagram showing an example of an open circuit voltage curve (measured value) and an open circuit voltage curve (estimated value).

If the open circuit voltage curve (actually measured value) and the open circuit voltage curve (estimated value) are obtained, the control device 14 calculates the voltage error Δ V and the capacity error Δ Q of both (S226). The voltage error Δ V may be, for example, the voltage error Δ V at a predetermined battery capacity α as shown in fig. 17, or may be a square average of the voltage errors between 2 open-circuit voltage curves, or the like.

The capacity error Δ Q may be an absolute value of a difference between the actually measured capacity Q1 and the estimated capacity Q2, that is, Δ Q | Q1 to Q2 |. As the actually measured capacity Q1, the current integrated value Δ Ah acquired in the parameter acquisition routine may be used₁₂. As the estimated capacity Q2, a capacity change amount when the open-circuit voltage curve (estimated value) changes from the first open-circuit voltage value Vo1 to the second open-circuit voltage value Vo2 may be used.

If the voltage error Δ V and the capacity error Δ Q are obtained, the controller 14 then calculates an evaluation function f (Δ V, Δ Q) for the voltage error Δ V and the capacity error Δ Q (S228). As the evaluation function f (Δ V, Δ Q), for example, a value obtained by weighted addition of the voltage error Δ V and the capacity error Δ Q may be used.

The controller 14 determines whether or not the evaluation function f (Δ V, Δ Q) calculated this time is smaller than the evaluation function f (Δ V, Δ Q) stored in the memory 28. Here, if the evaluation function f (Δ V, Δ Q) of this time is smaller than the evaluation function f (Δ V, Δ Q) stored in the memory 28, the evaluation function f (Δ V, Δ Q) of this time and the degradation parameter (k) of this time are set₁，k₂，ΔQ_s) Stored together in memory 28. Further, if the evaluation function f (Δ V, Δ Q) at this time is larger than the evaluation function f (Δ V, Δ Q) stored in the memory 28, the evaluation function f (Δ V, Δ Q) stored in the memory 28 is stored as it is.

In step S230, the control device 14 determines whether or not the degradation parameter has changed in all the search ranges (S230). If the degradation parameter is not changed in all the search ranges, the degradation parameter (k) is changed₁，k₂，ΔQ_s) And returns to step S224 (S229).

On the other hand, if the degradation parameter is changed in all the search ranges, the search is ended. At this time, the memory 28 stores the degradation parameter (k) having the smallest evaluation function f (Δ V, Δ Q) in the search range₁，k₂，ΔQ_s). The degradation parameter (k) stored in the memory 28₁，k₂，ΔQ_s) It can be said that it indicates the current battery 12A parameter of a degraded state. The control device 14 determines the degradation parameter (k) based on the determined degradation parameter₁，k₂，ΔQ_s) The SOC-OCV curve and the full charge capacity FCC are estimated, and the estimated values are stored in the memory 28 (S232).

In addition, the deterioration estimating routine shown in fig. 10 and 11 is an example, and the plurality of open-circuit voltage values Vo1 and Vo2 and the current integrated value Δ Ah between a plurality of points are used₁₂To estimate the state of degradation of the battery 12, other routines may be used.

As described above, in the battery system 10 disclosed in the present specification, the parameters (Vo1, Vo2, Δ Ah) acquired in the non-hysteresis region are used₁₂) To estimate the deterioration with age. This makes it possible to accurately estimate the deterioration of the battery 12 without being affected by the hysteresis. However, in order to estimate the deterioration of the battery 12 more accurately, the larger the acquisition interval of the parameters, i.e., the interval between the first open voltage value Vo1 and the second open voltage value Vo2, the better. Therefore, the first open voltage value Vo1 and the second open voltage value Vo2 are preferably taken near the upper end and near the lower end of the non-hysteresis region, if possible.

However, the range of the non-hysteresis region is expanded and reduced with the aging deterioration of the battery 12. This is explained with reference to fig. 18. In FIG. 18, the negative open circuit potential U_2＿iniAnd U_2＿aftIn the middle, the thick line shows the negative open-circuit potential after the battery is continuously charged, and the thin line shows the negative open-circuit potential after the battery is continuously discharged. In addition, the local charging rate theta is set so that the difference between the negative open-circuit potential after continuous charging (thick line) and the negative open-circuit potential after continuous discharging (thin line) is equal to or greater than a certain value_2BReferred to as "hysteresis occurrence point θ_2B”。

As described above, the open-circuit voltage value Vo of the battery 12 is the difference between the positive open-circuit potential and the negative open-circuit potential. In general, the charging rate Cb is set to 100% when the open circuit voltage value Vo of the battery 12 reaches the predetermined upper limit VH, and 0% when the open circuit voltage value Vo reaches the predetermined lower limit VL. The positive electrode capacity or the negative electrode capacity that changes from Vo to VL to Vo to VH is the full charge capacity FCC.

As shown in fig. 18, the negative open-circuit potential U is set from the initial state with the aged deterioration of the battery 12_2＿iniChanged to degraded negative open circuit potential U_2＿aft. In this case, it is known that: at a distance from theta_2LTo theta_2H(0% Cb or more and 100% Cb or less), a hysteresis occurrence point θ at full charge capacity FCC_2BIs different in the initial state and the degraded state. This indicates that the non-hysteresis region is changed due to the deterioration of the battery 12.

Thus, the actual non-hysteresis region expands and contracts due to the aged deterioration of the battery 12. In the parameter acquisition routine, various parameters Vo1, Vo2, Δ Ah are acquired in the non-hysteresis area stored in the memory 28₁₂. If the non-lag area stored in the memory 28 deviates from the actual non-lag area, it is actually probable that the parameters are acquired in the lag area. Of course, this problem can be avoided if the change in the actual non-hysteresis region due to the deterioration is estimated and the non-hysteresis region stored in the memory 28 is set from the beginning. However, in this case, the parameter acquisition range may be narrowed, and the opportunity for parameter acquisition may be reduced.

Therefore, the range of the non-hysteresis region may be estimated and updated every time the degradation estimation process of the battery 12 is performed. Specifically, the degradation parameter (k) acquired in the degradation estimation routine shown in fig. 11 is used₁，k₂Δ Qs) to determine the negative open circuit potential U after degradation_2＿aft. Thereby, the hysteresis generation point θ_2BOr theta_1BThe position of (c) and the value of the boundary charging rate Cb _ b that defines the boundary between the non-hysteresis region and the hysteresis region can be determined. Specifically, the boundary charging rate Cb _ b may be θ₁、θ₂The following expressions (11) and (12) are given.

Cb＿b＝(θ_2B－θ_2L)/(θ_2H－θ_2L) (11)

Cb＿b＝(θ_1H－θ_1B)/(θ_1H－θ_1L) (12)

The control device 14 determines the boundary charging rateThe non-lag area defined by Cb _ b is stored in the memory 28 as a new non-lag area and updated. By estimating and updating the current non-hysteresis region every time the aged deterioration is estimated, the first open-circuit voltage value Vo1, the second open-circuit voltage value Vo2, and the current integrated value Δ Ah can be acquired at appropriate timings (charging rates)₁₂. As a result, the accuracy of estimating the aged deterioration of the battery 12 can be further improved, and the opportunity of estimation can be obtained more reliably.

In addition, in equations (11) and (12), the local charging rate θ is determined according to₁、θ₂The boundary state of charge Cb _ b is estimated, but an SOC-OCV curve may be obtained from the deteriorated positive and negative open-circuit potentials, and the boundary state of charge Cb _ b may be obtained from the SOC-OCV curve.

Fig. 19 is a flowchart showing an example of the estimation routine of the non-hysteresis region. The non-hysteresis region estimation routine of fig. 19 is premised on being executed after the degradation estimation routine shown in fig. 11. Therefore, it is assumed that SOC-OCV curves after the aged deterioration (current state) of the battery 12, i.e., the deteriorated OCV _ dis and OCV _ ch, can be obtained.

When the voltage indicated by OCV _ dis is Vdis [ n ], the voltage indicated by OCV _ ch is Vch [ n ], and the predetermined threshold value is Δ Vdef when the charging rate Cb is equal to n, the control device 14 searches for a value satisfying (| Vdis [ n ] -Vch [ n ] | < Δ Vdef) while sequentially changing the value of the charging rate Cb equal to n (S312, S314). The start value of the search may be a value obtained by subtracting a predetermined margin α from the boundary state of charge Cb _ b obtained in the estimation of the last non-hysteresis region (S310). The boundary state of charge Cb _ b increases or decreases after the deterioration, depending on the characteristics of the battery. Therefore, the predetermined width α may be changed to a positive value or a negative value according to the characteristics of the battery. The search start value is not limited to this, and may be another value, for example, a predetermined fixed value. If the value n satisfying (| Vdis [ n ] -Vch [ n ] | < Δ Vdef) is found as a result of the search, the value n may be stored in the memory 28 as a new boundary charging rate Cb _ b (S316).

As is apparent from the above description, according to the battery system 10 disclosed in the present specification, the parameters necessary for estimating the aged deterioration of the battery 12 are acquired in the non-hysteresis region. As a result, the aged deterioration of the battery 12 can be accurately and easily estimated without being affected by the hysteresis. In addition, other configurations may be appropriately modified as long as parameters necessary for estimating the aged deterioration are acquired in the non-hysteresis region.

For example, in the above description, as parameters used in the aged deterioration estimation, only two open-circuit voltage values Vo1 and Vo2 and a current integrated value Δ Ah12 between the two points are acquired. However, if the parameter is in the non-hysteresis region, the open-circuit voltage values Vo at a plurality of points and the current integrated value Δ Ah between the plurality of points may be acquired.

In the present description, the battery 12 in which the negative electrode active material contains a silicon-based material and graphite is exemplified, but if the battery is a secondary battery having a partially significant hysteresis, the technique disclosed in the present description can be applied to other types of secondary batteries. For example, the technology disclosed in the present specification can also be applied to a lithium ion secondary battery in which the negative electrode active material contains a silicon-based material and lithium titanate. It is known that hysteresis occurs in a high SOC region in a lithium ion secondary battery containing a silicon-based material and lithium titanate. Therefore, when using this lithium ion secondary battery, the low SOC region may be set as a non-hysteresis region, and the aging degradation of the battery may be estimated using the parameters Vo and Δ Ah acquired in the low SOC region (non-hysteresis region). The technology disclosed in the present specification is not limited to lithium ion secondary batteries, and may be applied to other types of secondary batteries such as nickel hydrogen secondary batteries.

Further, hysteresis of SOC-OCV is likely to occur in a battery in which the active material contains a material having a large volume change (expansion and contraction). Examples of the negative electrode material include silicon-based (Si, SiO, etc.), tin-based (Sn, SnO), and germanium-based and/or lead-based compounds obtained by alloying lithium. Here, the volume change of graphite used as a negative electrode material of a lithium ion battery is generally about 10%. The "material having a large volume change" that causes hysteresis of SOC-OCV may be, for example, a material having a larger volume change than graphite (a larger volume change of 10%).

Alternatively, a transition material represented by the following formula (13) (e.g., CoO, FeO, NiO, Fe₂O₃Etc.) may also be used for the anode material. In formula (13), M represents a transition metal, and X represents O, F, N, S or the like.

nLi⁺+ne^-+Mⁿ⁺X^m←→M+nLiX_m/n(13)

In addition, FeF may be used for the positive electrode₃Such a transition material. In the present description, the case where the SOC-OCV hysteresis occurs due to the negative electrode material is exemplified, but the technique disclosed in the present description can be applied even when the hysteresis occurs due to the positive electrode material.

Claims

1. A battery system mounted on a vehicle includes:

a battery mounted on the vehicle and configured to be charged and discharged, wherein a charging rate range of the battery includes a hysteresis range in which a significant hysteresis occurs, the significant hysteresis being a hysteresis in which an open circuit voltage with respect to a charging rate of the battery has a certain or greater difference between after continuous charging and after continuous discharging, and a non-hysteresis range in which the significant hysteresis does not occur;

a voltage detector configured to detect a voltage of the battery as a detected voltage value;

a current detector configured to detect a current flowing in the battery as a detected current value;

a charger configured to charge the battery while the vehicle is stopped; and

an electronic control unit configured to control charging and discharging of the battery, the electronic control unit being configured to estimate aged deterioration of the battery based on an open-circuit voltage value calculated from the detected voltage value and a current integrated value calculated from the detected current value,

the electronic control unit is configured to estimate the aged deterioration of the battery based on the open-circuit voltage value and the current integrated value calculated when the charging rate of the battery is within the non-hysteresis region,

the open circuit voltage value includes a first open circuit voltage value and a second open circuit voltage value acquired in the non-hysteresis region,

the current integrated value is obtained by integrating the current values detected from the first open circuit voltage value to the second open circuit voltage value,

the electronic control unit is configured to estimate at least one of a current full charge capacity of the battery and a current change characteristic of the open voltage value with respect to the charging rate as a characteristic indicating the aged deterioration, based on the first open voltage value, the second open voltage value, and the current integrated value,

the electronic control unit is configured to temporarily stop charging by the charger when the charging rate of the battery reaches a first charging rate or a second charging rate in the non-hysteresis region during charging of the battery by the charger, and acquire the detected voltage value obtained during a charging stop period as the first open voltage value or the second open voltage value.

2. The battery system of claim 1,

the electronic control unit is configured to acquire, as the first open voltage value and the second open voltage value, two open voltage values acquired at a timing when the open voltage value is within the non-hysteresis region and can be acquired, during a period in which a power source of the vehicle is turned on.

3. The battery system of claim 1,

the electronic control unit is configured to control charging and discharging of the battery so that a charging rate of the battery shifts into the non-hysteresis region, and acquire the first open-circuit voltage value, the second open-circuit voltage value, and the current integrated value, when an elapsed time from last estimation of aged deterioration becomes equal to or longer than a predetermined reference time.

4. The battery system according to any one of claims 1 to 3,

the electronic control unit is configured such that,

estimating at least a change characteristic of an open-circuit voltage value with respect to the charging rate as a characteristic representing the aged deterioration;

estimating a state of charge range to be the non-hysteresis region based on the estimated change characteristic of the open circuit voltage value with respect to the state of charge;

updating the non-hysteresis region based on the estimated charge rate range.

5. The battery system of claim 4,

the electronic control unit is configured to update one of the ranges of the charging rate and the charging rate at the time of acquiring the open-circuit voltage value and the current integrated value for estimating the aged deterioration in accordance with the update of the non-hysteresis region.

6. The battery system according to any one of claims 1 to 3,

the battery is a lithium ion secondary battery in which a negative electrode active material contains at least a silicon-based material and graphite,

the non-hysteresis region has a higher charge rate range than the hysteresis region.

7. The battery system according to any one of claims 1 to 3,

the battery is a lithium ion secondary battery in which a negative electrode active material contains at least a silicon-based material and lithium titanate,

the non-hysteresis region has a lower charge rate range than the hysteresis region.

8. An aged deterioration estimation method of a battery system, the charging rate range of the battery including a hysteresis region and a non-hysteresis region, the hysteresis region being the charging rate range in which significant hysteresis occurs, the significant hysteresis being hysteresis in which there is a certain or more difference in an open circuit voltage with respect to the charging rate of the battery after continuous charging and after continuous discharging, the non-hysteresis region being the charging rate range in which the significant hysteresis does not occur, the battery system including an electronic control unit and a charger that charges the battery during a stop of a vehicle,

the method for estimating chronological deterioration includes:

acquiring a parameter by which an open circuit voltage value between two points and a current integrated value between the two points are calculated when a charging rate of the secondary battery is within the non-hysteresis region; and

estimating, by the electronic control unit, deterioration of the battery with age based on the acquired open-circuit voltage value and the current integrated value,

estimating, by the electronic control unit, at least one of a present full charge capacity of the battery and a change characteristic of an open voltage value with respect to the charging rate as a characteristic indicating the aged deterioration based on the first open voltage value, the second open voltage value, and the current integrated value,

when the charging rate of the battery reaches a first charging rate or a second charging rate in the non-hysteresis region during charging of the battery by the charger, the electronic control unit temporarily stops charging by the charger, and acquires the open-circuit voltage value obtained during a charging stop period as the first open-circuit voltage value or the second open-circuit voltage value.